v1.15 DX & Adoption: presets, traceability, reference examples

[maxches99]

Summary

• add NetworkClientPreset with restHeavy, realtimeHeavy, offlineFirst
• add merge-safe override points via NetworkClientPreset.RequestOverrides
• add runtime policy helper applyRuntimePolicy(from:scope:)
• add reference examples for auth refresh, reconnect recovery, offline replay, diagnostics
• add v1.15 traceability pack and v1.15 What's New
• include requested deletion of docs/REALTIME_INCIDENT_TRIAGE_v1.13.md

Requirement/Test mapping

• FR-1/FR-3: presetsExposeSafeDefaultsAndTradeoffs
• FR-4/EC-1: presetRequestOverridesMergeWithoutDroppingSafetyDefaults
• AR-1/EC-2: applyRuntimePolicyFromPresetEmitsPolicyUpdateTelemetry

Validation

• swift build
• swift test
• RUN_E2E_TESTS=1 swift test --enable-code-coverage --filter E2ECoverageTests
• swift test --enable-code-coverage + llvm-cov total line coverage: 92.30%

Notes

• v1.15 DFR document intentionally excluded from this PR per request.